The exact determination of the load mass of a load raised by a crane is of great importance for a plurality of applications: e.g. the load mass is important for the load moment limitation system of the crane, that is, for the tilt protection and for the structural protection. In addition, the load mass is of great importance for the data acquisition with respect to the performance of the crane. The total payload to be transferred can in particular be determined by an exact determination of the load mass. The load mass is furthermore also of great importance as a parameter for other control tasks at the crane such as a load swing damping.
A common method for determining the load mass is the measurement of the cable force in the hoist cable. The cable force in the hoist cable in this respect substantially corresponds to the load mass at least in a static state.
The measurement arrangement for measuring the cable force can in this respect be positioned either directly at the load suspension means. This positioning at the load suspension means has the advantage that only a few disturbing influences are present here and a greater precision can thus be achieved. The disadvantage of this solution is, however, that a power supply and a corresponding signal line to the load suspension means are necessary.
A further possibility is the positioning of a measurement arrangement in a connection region between the crane structure and the hoist cable, for example at a deflection pulley or at the hoisting gear. This has the advantage that the measurement arrangement can be made very robust and the cabling is relatively simple. It is disadvantageous in this arrangement of the measurement arrangement that further disturbing influences make an exact determination of the load mass from the cable force more difficult, particularly during dynamic conditions.
In this respect, it is already known to use mean (averaging) filters for determining the cable force. On the one hand, this has the disadvantage, however, that a relatively high delay in the signal output has to be accepted. On the other hand, a plurality of disturbing influences cannot be eliminated via a mean filter.
It is therefore the object of the present disclosure to provide a system for determining the load mass of a load carried by the hoist cable which allows an improved determination of the load mass based on the cable force.
This object is achieved in accordance with the present disclosure by a system for determining the load mass of a load carried by a hoist cable of a crane comprising a measurement arrangement positioned for measuring the cable force in the hoist cable and a calculation unit for determining the load mass on the basis of the cable force. In accordance with the present disclosure, the calculation unit has a compensation unit which describes the influence of the indirect determination of the load mass via the cable force in a model and at least partly compensates it when determining the load mass.
Provision can be made, on the one hand, in this respect that the compensation unit at least partly compensates static influences of the indirect determination of the load mass via the cable force. For this purpose, in accordance with the present disclosure, the static influences of the indirect determination are modeled and compensated by the compensation unit. A substantially more precise determination of the load mass hereby results which was not possible at all via mean value filters since they cannot eliminate static influences at all.
Provision can alternatively or additionally be made that the compensation unit also at least partly compensates dynamic influences of the indirect determination of the load mass via the cable force. Provision is also made for this purpose that the compensation unit models the dynamic influences and compensates the load mass in the determination.
Provision is advantageously made in accordance with the present disclosure that the compensation unit is based on a physical model of the lifting procedure which models the static and/or dynamic influences of the indirect determination of the load mass via the cable force. The compensation unit can at least partly compensate these static and/or dynamic influences by this model.
Provision is advantageously made in this respect that the compensation unit works on the basis of data on the position and/or movement of the crane.
In this respect, data on the position and/or movement of the hoisting gear and/or data on the position and/or movement of the boom and/or of the tower are advantageously included in the compensation unit,
The system in accordance with the present disclosure is in particular used in this respect in derrick boom cranes in which a boom can be luffed up and down about a horizontal luffing axis and can be rotated via a tower or superstructure about a vertical axis of rotation.
Provision is advantageously made in this respect that the measurement arrangement is arranged in a connection element between an element of the crane structure and the hoist cable, in particular at a deflection pulley or at the hosting gear. Provision is advantageously made in this respect that the compensation unit at least partly compensates static and/or dynamic influences of the arrangement of the measurement arrangement. The compensation unit in this respect advantageously compensates the influences of the arrangement of the measurement arrangement on the cable force.
Provision is advantageously made in this respect that the compensation unit includes a cable mass compensation which takes account of the hoist cable's net weight. The hoist cable has a net weight which is not to be neglected and which no longer falsifies the determination of the load mass due to the present disclosure. The compensation unit in this respect advantageously takes account of the influence of the change in the cable length on the raising and/or lowering of the load in the calculation of the load mass. The net weight of the hoist cable has a different influence on the cable force in dependence on the lifting phase due to the change in the cable length. The system in accordance with the present disclosure takes this into account.
The system is in this respect advantageously used in a hoisting gear which includes a winch, with the angle of rotation and/or the speed of rotation of the winch being included in the cable mass compensation as an input value. The cable length and/or the cable speed can be determined on the basis of the angle of rotation and/or on the speed of rotation and its/their influence on the cable force can be taken into account in the calculation of the load mass.
Alternatively, the cable length and/or the cable speed can also be determined via a measurement roll. It can e.g. be arranged separately at the cable or can be made as a deflection pulley.
Provision is further advantageously made that the cable mass compensation takes account of the net weight of the hoist cable wound up on the winch. This is in particular of advantage when the measurement arrangement is arranged at the hoist winch for the measurement of the cable force, in particular at a torque support of the hoist winch since then the cable wound up on the winch is supported on the measurement arrangement and thus influences the measured values.
Provision is further advantageously made that the cable mass compensation takes account of a length of hoist cable sections changing by the movement of the crane structure and/or takes account of the alignment of hoist cable sections. This is in particular of importance in such cranes in which the hoist cable system changes its length or alignment on a movement of the crane structure, in particular on a movement of the boom. This is in particular the case when the cable is not guided parallel to the boom at the crane, but rather when the cable adopts an angle to the boom which changes by a luffing up and down of the boom. Depending on the position of the crane structure, in particular of the boom, different lengths and/or alignments of the sections of the hoist cable thus result, which in turn influence the effect of the net weight of the hoist cable on the output signal of the measurement arrangement.
Provision is further advantageously made that the compensation unit includes a deflection pulley compensation which takes account of friction effects due to the deflection of the hoist cable about one or more deflection pulleys. In this respect, in particular the bending work required for the deflection of the hoist cable is advantageously taken into account as a friction effect. Alternatively or additionally, the roll friction in the deflection pulleys can also be taken into account.
Provision is advantageously made in this respect that the deflection pulley compensation takes account of the direction of rotation and/or of the speed of rotation of the deflection pulleys. In particular the direction of rotation in this respect has a not insubstantial influence on the cable force.
The deflection pulley compensation in this respect advantageously calculates the direction of rotation and/or the speed of rotation of the deflection pulleys caused by the movement of the crane structure and the movement of the hoisting gear. In particular with multiaxial deflection pulleys of the hoist cable between the tower and the boom, complicated movement patterns can result here which have a corresponding effect on the output signal of the measurement arrangement.
The deflection pulley compensation in this respect advantageously determines the friction effects in dependence on the measured cable force. The cable force has a decisive influence on the friction effects. In this respect, the friction effects are advantageously determined on the basis of a linear function of the measured cable force since a linear function represents a relatively good approximation of the physical situation.
Further advantageously, provision is made in the system in accordance with the present disclosure that the compensation unit takes account of the influence of the acceleration of the load mass and/or of the hoisting gear on the cable force in the determination of the load mass. The acceleration of the load mass and/or of the hoisting gear in this respect generates a dynamic component of the hoist force which is at least partly compensated by the compensation in accordance with the present disclosure. The compensation unit in this respect advantageously works on the basis of a physical model which describes the influence of the acceleration of the load mass and/or of the hoisting gear on the cable force.
Provision is further advantageously made that the calculation unit takes account of the oscillation dynamics, which arise due to the elasticity of the hoist cable, in the determination of the load mass. In addition to the accelerations which are caused by the accelerations induced via the hoisting gear, the system of cable and load additionally has oscillation dynamics which arise due to the elasticity of the hoist cable. The compensation unit advantageously at least partly compensates these oscillation dynamics. The compensation unit for the compensation of the oscillation dynamics is in this respect advantageously based on a physical model.
The calculation unit of the system in accordance with the present disclosure in this respect advantageously includes a load mass observer which is based on a spring mass model of the cable and of the load. The mass of the actual load as well as the mass of the load suspension means and of the slings are in this respect advantageously described in the model. In contrast, the cable between the winch and the load suspension means is included as a spring in the model.
The load mass observer in this respect advantageously constantly compares the measured cable force with the cable force predicted with reference to the spring-mass model on the basis of the previously measured cable force. On the basis of this comparison, the load mass observer estimates the load mass of the load which is included as a parameter in the spring-mass model of the cable and of the load. The load mass can hereby be determined with high precision and with compensation of dynamic influences.
The load mass observer in this respect advantageously takes account of the measurement noise of the measured signals. A white noise free of mean values is advantageously used for this purpose.
Data on the length of the cable are advantageously included as measured signals in addition to the output signal of the measurement arrangement for determining the cable force. In this respect, a cable force normalized with respect to the permitted maximum load is advantageously used as a parameter of the load mass observer.
The present disclosure furthermore includes a crane having a system for the determination of the load mass of a load carried by a hoist cable, as was presented above. The crane is in this respect in particular a boom crane in which the boom can be luffed up and down about a horizontal luffing axis. Further advantageously, the crane can be rotated about a vertical axis of rotation. The boom is in this respect in particular pivotally connected to a tower which is rotatable about a vertical axis of rotation with respect to an undercarriage. The boom can in this respect in particular be a harbor mobile crane. The system in accordance with the present disclosure can, however, likewise be used in other crane types, e.g. in gantry cranes or tower slewing cranes.
In this respect, the system could advantageously be used in a crane in which the measurement arrangement for measuring the cable force is arranged in a connection element between an element of the crane structure and the hoist cable; in particular in a deflection pulley or at the hoisting gear. A very robust arrangement hereby results which nevertheless enables an exact determination of the load mass due to the system in accordance with the present disclosure.
In this respect, a plurality of applications are possible by the system in accordance with the present disclosure which were not able to be realized with known inaccurate systems. For example, a slack cable recognition can be installed which recognizes that the load was put down on the basis of the system in accordance with the present disclosure. An immediate switching off of the hoisting gear is thereupon initiated which prevents cable damage due to unwound cables. Mechanical slack cable switches can hereby optionally be dispensed with. In addition, a recognition of very small loads is now likewise possible such as of empty containers.
The system in accordance with the present disclosure furthermore has the great advantage over mean filters that the load mass can be determined without larger delay. A higher turnover hereby results since fewer stops occur when the load mass signal is used for the load moment limitation system. In addition, the service life of the crane is increased since the load moment limitation system can intervene without any greater time delay.
In addition to the system and to the crane, the present disclosure further comprises a method for determining the load mass of a load carried by the hoist cable, comprising the steps: measuring the cable force in the hoist cable; calculating the load mass on the basis of the cable force; wherein the influence of the determination of the load mass via the cable force is described in a model and is at least partly compensated.
The compensation in this respect in particular takes place on the basis of a model of the static and/or dynamic influences of this determination. These influences can hereby be calculated and can be at least partly compensated by the compensation unit.
The method in accordance with the present disclosure advantageously takes place as was represented above with respect to the system and to the crane. The method in accordance with the present disclosure in this respect in particular takes place by means of a system as was described above.
The present disclosure will now be explained in more detail with reference to embodiments and to drawings.